1 /*
2 * Copyright (c) 2020, 2021, Amazon.com, Inc. and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25 #include "precompiled.hpp"
26 #include "gc/shenandoah/shenandoahCardTable.hpp"
27 #include "gc/shenandoah/shenandoahHeap.inline.hpp"
28 #include "gc/shenandoah/shenandoahUtils.hpp"
29
30 void ShenandoahCardTable::initialize() {
31 CardTable::initialize();
32 _write_byte_map = _byte_map;
33 _write_byte_map_base = _byte_map_base;
34 const size_t rs_align = _page_size == (size_t) os::vm_page_size() ? 0 :
35 MAX2(_page_size, (size_t) os::vm_allocation_granularity());
36
37 ReservedSpace heap_rs(_byte_map_size, rs_align, _page_size);
38 if (!heap_rs.is_reserved()) {
39 vm_exit_during_initialization("Could not reserve enough space for second copy of card marking array");
40 }
41 os::commit_memory_or_exit(heap_rs.base(), _byte_map_size, rs_align, false, "Cannot commit memory for second copy of card table");
42
43 HeapWord* low_bound = _whole_heap.start();
44 _read_byte_map = (CardValue*) heap_rs.base();
45 _read_byte_map_base = _read_byte_map - (uintptr_t(low_bound) >> card_shift());
46
47 log_trace(gc, barrier)("ShenandoahCardTable::ShenandoahCardTable: ");
48 log_trace(gc, barrier)(" &_read_byte_map[0]: " INTPTR_FORMAT " &_read_byte_map[_last_valid_index]: " INTPTR_FORMAT,
49 p2i(&_read_byte_map[0]), p2i(&_read_byte_map[last_valid_index()]));
50 log_trace(gc, barrier)(" _read_byte_map_base: " INTPTR_FORMAT, p2i(_read_byte_map_base));
51
52 // TODO: As currently implemented, we do not swap pointers between _read_byte_map and _write_byte_map
53 // because the mutator write barrier hard codes the address of the _write_byte_map_base. Instead,
54 // the current implementation simply copies contents of _write_byte_map onto _read_byte_map and cleans
55 // the entirety of _write_byte_map at the init_mark safepoint.
56 //
57 // If we choose to modify the mutator write barrier so that we can swap _read_byte_map_base and
58 // _write_byte_map_base pointers, we may also have to figure out certain details about how the
59 // _guard_region is implemented so that we can replicate the read and write versions of this region.
60 //
61 // Alternatively, we may switch to a SATB-based write barrier and replace the direct card-marking
62 // remembered set with something entirely different.
63
64 resize_covered_region(_whole_heap);
65 }
66
67 bool ShenandoahCardTable::is_in_young(const void* obj) const {
68 return ShenandoahHeap::heap()->is_in_young(obj);
69 }
70
71 bool ShenandoahCardTable::is_dirty(MemRegion mr) {
72 for (size_t i = index_for(mr.start()); i <= index_for(mr.end() - 1); i++) {
73 CardValue* byte = byte_for_index(i);
74 if (*byte == CardTable::dirty_card_val()) {
75 return true;
76 }
77 }
78 return false;
79 }
80
81 size_t ShenandoahCardTable::last_valid_index() {
82 return CardTable::last_valid_index();
83 }
84
85 void ShenandoahCardTable::clear() {
86 CardTable::clear(_whole_heap);
87 }
88
89 // TODO: This service is not currently used because we are not able to swap _read_byte_map_base and
90 // _write_byte_map_base pointers. If we were able to do so, we would invoke clear_read_table "immediately"
91 // following the end of concurrent remembered set scanning so that this read card table would be ready
92 // to serve as the new write card table at the time these pointer values were next swapped.
93 //
94 // In the current implementation, the write-table is cleared immediately after its contents is copied to
95 // the read table, obviating the need for this service.
96 void ShenandoahCardTable::clear_read_table() {
97 for (size_t i = 0; i < _byte_map_size; i++) {
98 _read_byte_map[i] = clean_card;
99 }
100 }
101
102 // TODO: This service is not currently used because the mutator write barrier implementation hard codes the
103 // location of the _write_byte_may_base. If we change the mutator's write barrier implementation, then we
104 // may use this service to exchange the roles of the read-card-table and write-card-table.
105 void ShenandoahCardTable::swap_card_tables() {
106 shenandoah_assert_safepoint();
107
108 CardValue* save_value = _read_byte_map;
109 _read_byte_map = _write_byte_map;
110 _write_byte_map = save_value;
111
112 save_value = _read_byte_map_base;
113 _read_byte_map_base = _write_byte_map_base;
114 _write_byte_map_base = save_value;
115
116 // update the superclass instance variables
117 _byte_map = _write_byte_map;
118 _byte_map_base = _write_byte_map_base;
119 }